1. Field of the Invention
The present invention relates to an optical disc system, and more particularly, to a tracking balance correction apparatus for use in an optical disc system using a tracking servo method of obtaining a tracking error signal via differential phase detection.
2. Description of the Related Art
An optical disc system irradiates a laser beam on an optical disc on which information is recorded and detects a beam reflected from the surface of the disc, to then reproduce a signal using the detected beam. A digital versatile disc (DVD) or a compact disc (CD) records information through a cavity called a pit. Therefore, when controlling tracking servo in order to accurately trace using a laser beam with respect to successive pits, the optical disc system should adjust tracking balance to make the laser beam be positioned in the middle of a pit. Prior art relating to tracking balance is disclosed in Korean Patent Application No. 96-51271 assigned to the same assignee.
Korean Patent Application No. 96-51271 discloses a method employed in a tracking servo technique for detecting the distribution of an intensity of light varied with a relative position of a beam irradiated on a disc and a pit of the disc using an optical detector including four light receiving elements, and for generating a tracking error signal based on a differential phase between diagonal summing signals each being obtained from the signals detected by the light receiving elements located on a diagonal line. According to the method disclosed in that application, a digital signal processor receives a tracking error signal, generates a correction voltage which makes a value of the tracking error signal be set to zero, and delays a diagonal summing signal according to the correction voltage to fit the phases of two diagonal summing signals. As a result, tracking balance is corrected.
However, even though the phases of the diagonal summing signals detected by the optical detector are in accord, it is not always that a beam is placed in the middle of a pit. This will be described in more detail with reference to FIGS. 1A and 1B.
In case of FIG. 1A showing that the center of a beam `b ` is placed in the middle of a pit `p`, the phases of diagonal summing signals A and B are in accord. In case of FIG. 1B showing the center of a beam `b` is placed in the brim of a pit `p`, tracking balance is not in accord, but the phases of diagonal summing signals A and B are in accord. Consequently, there is a drawback that the tracking balance cannot completely be corrected using only the differential phase of the diagonal summing signals.